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Robot battery runtime calculator

Estimates runtime from pack capacity and average draw, and separately checks the peak draw against what the pack is rated to deliver — which is the question that actually explains a brownout.

The question this answers: “How long will this pack run my robot, and is it the reason the board keeps resetting?”

Printed on the pack.

Whole robot while running. Measure it if you can \u2014 this is the input the answer is most sensitive to.

Under load \u2014 climbing, stalling, or a weapon spinning up.

Your choice, not this tool\u2019s. Running a pack near empty is where cell damage happens.

Continuous discharge rating printed on the pack.

Result

Estimated runtime
52.8 min
1760 mAh usable of 2200 mAh, at 2 A average.
Usable capacity
1760 mAh
80% of the pack, which is your choice rather than this tool's.
Pack continuous rating
55 A
2.2 Ah × 25C. Compare against your peak draw, not your average.
Peak draw against that rating
15%
Under the rating. Sag is still possible near the top of this range.

Worth knowing about this answer

  • A first-order estimate from an average current, and the average is the part you are guessing at. Real draw varies constantly with terrain, load and how much the motors are stalling, and a robot that spends time pushing against something draws far more than one driving freely.
  • This tool gives no charging guidance, no voltage limits and no cell-count advice. Those are properties of your specific pack and belong to its manufacturer.
Show the working
  1. Capacity in amp-hours2200 mAh ÷ 10002.2 Ah
  2. Usable capacity2.2 × 80%1.76 Ah
  3. Runtime1.76 Ah ÷ 2 A × 6052.8 min
  4. Continuous current available2.2 Ah × 25C55 A

Estimated runtime: 52.8 min. Usable capacity: 1760 mAh. Pack continuous rating: 55 A. Peak draw against that rating: 15%

How it works

Capacity is converted from milliamp-hours to amp-hours and multiplied by the proportion you choose to use. Runtime is that usable capacity divided by the average current, converted to minutes. Separately, the pack’s continuous current capability is its capacity in amp-hours multiplied by its C rating, and the peak draw is expressed as a percentage of that — which is what indicates whether voltage sag under load is likely.

What it assumes

  • A constant average current, which is a simplification of a draw that varies continuously with terrain and load.
  • The C rating printed on the pack is accurate, which is not reliably true of budget cells.
  • The usable proportion is the operator’s choice rather than a recommendation, and is an input for exactly that reason.

Where it stops being reliable

  • The answer is only as good as the average current, which is the input people guess at. A robot that spends time pushing against something draws far more than one driving freely, and measuring beats estimating by a wide margin.
  • It gives no charging guidance, no voltage limits and no cell-count advice. Those are properties of a specific pack and belong to its manufacturer — the robotics page declines to publish them for the same reason.
  • Capacity falls with temperature and with age, and neither is modelled.
  • The headroom check indicates whether sag is likely; it cannot tell you that a particular robot will or will not brown out, which depends on wiring, decoupling and how the supplies are arranged.

Runs entirely in your browser — nothing you type is sent anywhere. Last reviewed 2026-08-16. More on Robotics.